1. Field of the Invention
The present invention relates to a serial interface for a microcontroller or microprocessor. More particularly, the present invention relates to a two line serial interface between a microprocessor or microcontroller and a peripheral device, such as a hearing aid, that does not require that an address be provided to the peripheral device.
2. The Prior Art
In well-known methods of acoustically fitting a hearing compensation device such as a hearing-aid to an individual, the hearing profile of the individual's hearing is typically measured using an audiometer generating pure tones at various frequencies between 125 Hz and 12,000 Hz that are representative of the frequency bands the tones are included in. These tones are transmitted to the individual being tested to determine the amount of amplification, compression, and/or other adjustment that will be employed to compensate for the individual's loss of hearing.
When the audiometer apparatus includes earphones to supply the tones to an individual being tested, it is difficult to calibrate the output of the hearing-aid device to be worn by the individual to match the output of the headphones which were used to measure the hearing loss. Another problem associated with the use of headphones to present tones to the individual is that due to the unique acoustics of each individual's ear canal, the acoustic response and therefore the perception by the individual of the sound provided by the headphones will be different from the perception of sound when the actual hearing-aid device is inserted into the ear canal.
Finally, once the hearing compensation provided by the hearing-aid has been set, and the hearing-aid has been inserted into the ear canal of the individual, the testing methods do not provide any satisfactory manner of performing an instantaneous comparison between a first fitting and a second fitting. This is known as A-B comparison. Typically, the amount of time required to perform an A-B comparison is either the amount of time needed to remove a device A and insert a second device B, or the 20 plus seconds required to update the programmed hearing compensation in a programmable hearing aid. This makes it difficult for an individual to accurately compare perceived differences in loudness in response to stimuli for the alternate fittings.
To overcome the problems associated with an audiometer apparatus that either employs headphones or a generic device that is fits into the ear to test for hearing loss, Sonic Innovations, Inc. has developed a fitting system that employs a programmable hearing aid to be worn by the individual as the means of generating the tones used to assess the hearing loss. In addition to being programmable to set the parameters for the signal processing circuits in the hearing that provide hearing compensation, the hearing aid may also be various circuit component in the hearing aid may be trimmed to compensate for variation in the electrical characteristics of the components employed in a hearing aid.
Since the data to generate the tones, program the hearing compensation and trim the components of the hearing aid must be written into the actual hearing aid that the user will wear, the interface between the device providing the data and the hearing aid should have a minimum number of pins and be very efficient due to size and data transmission time constraints. There are several known serial interfaces that are employed in microcontrollers, including the I.sup.2 C from Phillips Electronics Eindhoven, Netherlands, SPI from Motorola, Schaumberg, Ill., and micro-wire, from National Semiconductor, Santa Clara, Calif. Typically these serial interfaces require that the data sent over the serial interface includes an address for the data and further, that the data have a fixed word length. This presents a disadvantage in systems where data transmission time and size constraints are important, because more data is sent than is needed, and additional circuits are required to process the unnecessary data.